LE SPHINX 1 was a pocket cryptographic device,
developed around 1930 by
Société des Codes Télégraphiques Georges Lugagne
in Paris (France).
The device consists of 10 sliding bars with two scrambled alphabets each,
and should therefore be classed as an alphabet transposition cipher.
At the time, it was advertised as a method for secret writing when sending
(radio) telegrams.

The device consists of a metal frame with ten lanes, each
of which holds two movable rods with scrambled alphabets.
The 20 transposed alphabets are
identified by a number, imprinted in red, and are always used in pairs,
with the upper alphabet representing the clear text and the lower alphabet
used for the cipher text. 2

The rods can be moved by treaded knobs at the right side which engage
gears at the bottom. Two fixed ruler windows are present for setting
and reading the plain text and cipher text.
The source text is processed 10 characters at a time.

The device is based on the 1912 invention of a mechanical pocket transposition
cipher device by Georges Lugagne of Boches-du-Rhône (near Marseille, France), which was registered in 1913 as
French Patent 461.217[1].
Around the same time, the device was patented in the United Kingdom
as British patent 23,204[2].
The device was marketed in France by Lugagne's companies in Paris
and Marseille, who had become known for their
international telegraphic code books of 1914.

The image on the right shows the original design of 1912, which is
mechanically less complex, but works very similar. It also consists
of 20 paired scrambled alphabets, but they are not coupled mechanically.
The sliding rods are made of ivory.

In 1931, the design was improved by Lugagne's employee Paul Godillon,
who added the gears and the 10 treaded knobs at the
right hand side. He was also responsible for adding the
S-shaped gaps
at each end of the alphabet rods, allowing the scrambled alphabets
to be coupled in pairs, freely mixing the upper and lower alphabets.

The diagram below gives an overview of the various features of Le Sphinx.
The device measures just 162 x 87 x 20 mm and consist of a die-cast metal
alloy frame with 10 cogwheel driven lanes, each of which accomodates two
physically locked scrambled alphabets. This effectively results in 10
different transposition ciphers that allow the text to
be enciphered in groups of 10 letters.

On top of the device are two horizontal windows: one for the plaintext
and one for the ciphertext. The position of the rods or rulers
with the alphabets can be altered by means of 10 treaded knobs at the right
side. Each knob drives a cogwheel that in turn engages the teeth at the bottom
of a rod. Each position has a 'click' to ensure that the letters are
properly shown in the windows.

Name
Le Sphinx

The pocket cryptographic device featured on this page, was marketed by
Société des Codes Télégraphiques Georges Lugagne, which
had offices in Paris and Marseille (France). It is currently unclear under
what name the device was sold, but since the bakelite storage case holds
a raised image of a sphinx, it is commonly referred to as SPHINX.
The metal label at the left side of the device shows the company name
and the image of the sphinx, with the text 'LE SPHINX' (the sphinx).
In order to distinguish it from the
Sphinx Cipher Machine,
we will call it 'Le Sphinx'.

The name 'Sphinx' originates from the Greek language and represents
a mythical creature that generally consists of the body of a lion with
the head of a human. In Greek tradition it may also have the wings of
a bird. Sphinx' also exist in Egyptian culture (e.g. Great Sphinx of Giza) [9].

Permutations

When calculating the total number of combinations that can be made
with the device, we will first look at the original design of 1912.
It had 20 alphabet rulers, 10 of which were intended as the upper
alphabets and the other 10 were the lower alphabets [1]. This gives
us 10! (or 3,628,800) possible combinations of alphabets 1
for the upper half only.
As the same is true for the lower half, the total number of
combinations would be 3,628,800 x 3,628,800, which is no less than:

13,168,189,440,000

After the design had been improved by Paul Godillon in 1931, there
was no longer a differece between the upper and the lower alphabets,
allowing them to be mixed freely [3]. As a result the total number
of combinations in which the 20 alphabets can be mixed,
increased to 20! or:

Before exchanging a message by means of Le Sphinx, both parties first have
to agree which alphabet is used in each position. This is done by quoting
the red number that is printed on the top of each rod. This is known as the
settings or the key and is usually pre-arranged between the
parties. For the default position, which we have used on this page, the
key would be:

01 02 03 04 05 06 07 08 09 10

11 12 13 14 15 16 17 18 19 20

Both users should now install the alphabets in the order indicated on the
key sheet. Each pair (e.g. 01-11) should be coupled by fitting the S-shaped
gap at the top of the lower alphabet into the S-shaped gap at the bottom of
the upper alphabet. For the above key, the setup would be:

Le Sphinx is constructed in such a way that the user can move the rulers
by means of treaded knobs at the right side. There are 5 sets of two knobs.
The leftmost knobs (i.e. the larger ones) are used to control the rightmost
5 lanes, whilst the rightmost knobs control the leftmost 5 lanes.
Furthermore, there are two windows through which we can read a row of letters.
Now rotate the knobs so that the first 10 letters of the
plaintext
are visible in the upper window, for example:

TOPSECRETS

All you now have to do is read the
ciphertext
from the lower window, which in this case is:

IRUVPYQHWB

All the receiving party has to do, is rotate the rulers so that the ciphertext
is visible in the lower window. The original plaintext can now be read from
the upper window.

Despite the large number of possible arrangements of the alphabets,
Le Sphinx provides only low-grade cipher security. This is mainly caused
by the fact that the arrangment of the alphabets does not change during
the course of a message. If a message is long enough, it can be
solved by frequency analysis. For very short messages, the cipher would
be relatively secure though.

Another weakness of the system is that there is no provision for sending the
key at the start of a message. Instead, it has to be pre-arranged.
This was also the case with the German
Enigma cipher machine, although in
that case, procedures were in place to add a random message key.

Alphabets

The table below shows each of the 20 scrambled alphabets of our device.
Note that the alphabets are printed in the regular order, but that they
are shifted by a few positions on each ruler. Also note that the alphabets
on the first 10 rulers (1-10) are in ascending order, whilst the alphabets
on the last 10 rulers (11-20) are in descending order.